Process for treating elemental sulphur for smell improvement

ABSTRACT

A process for treating a stream of elemental sulphur comprising an organic polysulphide and/or a thiol for smell improvement, the process comprising the following steps: (a) providing a molten stream of elemental sulphur comprising an organic polysulphide and/or a thiol at a temperature in the range of from 120 to 160° C.; (b) admixing a liquid unsaturated compound with the stream of molten elemental sulphur in an amount in the range of from 0.01 to 10.0 wt % based on the weight of sulphur to allow the organic polysulphide and/or thiol to react with the unsaturated compound.

FIELD OF THE INVENTION

The invention provides a process for treating a stream of elementalsulphur comprising an organic polysulphide and/or a thiol for smellimprovement.

BACKGROUND OF THE INVENTION

Elemental sulphur is a by-product of oil and gas refining processes. Itis known that elemental sulphur obtained as a by-product of oil and gasrefining may be used as raw material for sulphuric acid or as a binderin sulphur cement or in other sulphur cement products, for examplesulphur cement-aggregate composites like sulphur mortar, sulphurconcrete or sulphur-extended asphalt.

In refineries, sulphur compounds in liquid hydrocarbonaceous streams aretypically converted by reaction with hydrogen into hydrogen sulphide.Thus, a gaseous stream comprising hydrogen sulphide and hydrogen isobtained. The hydrogen sulphide separated from this gaseous stream orhydrogen sulphide separated from natural gas is typically converted intoelemental sulphur. A well-known example of such process is the so-calledClaus process.

Conversion of hydrogen sulphide into elemental sulphur using the Clausprocess has certain disadvantages. The oxidation step in the Clausprocess is not selective for hydrogen sulphide, therefore separation ofthe hydrogen sulphide from the remainder of the gas stream is necessary.In view of thermodynamic limitations, no complete conversion of hydrogensulphide in a single process stage can be obtained.

An alternative for the Claus process is selective oxidation of hydrogensulphide comprised in a hydrocarbonaceous gas stream. Selectiveoxidation processes are disclosed in for example U.S. Pat. No.4,886,649, U.S. Pat. No. 4,311,683, U.S. Pat. No. 6,207,127 andWO2005/030638. Compared to the Claus process, selective oxidation hasseveral advantages. An advantage is that a high conversion of hydrogensulphide can be obtained in a single process stage. Another advantage isthat the oxidation is selective for hydrogen sulphide, thus avoiding theneed for separation of hydrogen sulphide from the other gas components.

In WO2005/030638 is disclosed a process for the selective oxidation ofhydrogen sulphide by contacting a hydrogen sulphide containing feed gasand molecular-oxygen containing gas with a particulate oxidationcatalyst in the presence of liquid elemental sulphur. The liquidelemental sulphur acts as an inert liquid medium that absorbs the heatgenerated by the exothermic oxidation reaction and thus prevents sulphurpolymerisation and clogging of the catalyst or reactor due to anincrease in sulphur viscosity.

In the selective oxidation process as described in WO2005/030638, astream of liquid elemental sulphur, optionally containing catalystparticles, might be discharged from the selective oxidation reactor.Such elemental sulphur could for example be used as a binder in sulphurcement or in other sulphur cement products. It has, however, been foundthat in case the hydrogen sulphide containing feed gas comprises thiols,the elemental sulphur that might be discharged from the selectiveoxidation reactor has an obnoxious smell. This smell is believed to bedue to the presence of organic polysulphides that are formed from thethiols during the oxidation process. Also unconverted thiols remainingin the elemental sulphur might contribute to this smell. This smelldisadvantageously limits the applicability of elemental sulphurobtainable from the selective oxidation process as described inWO2005/030638.

SUMMARY OF THE INVENTION

It has now been found that the obnoxious smell of elemental sulphur thatcontains organic polysulphides and/or thiols can be removed ordiminished to an acceptable level by adding a small amount of anunsaturated compound to the elemental sulphur whilst the elementalsulphur is kept at a temperature in the range of from 120 to 160° C.

Accordingly, the invention provides a process for treating a stream ofelemental sulphur comprising an organic polysulphide and/or a thiol forsmell improvement, the process comprising the following steps:

(a) providing a molten stream of elemental sulphur comprising an organicpolysulphide and/or a thiol at a temperature in the range of from 120 to160° C.;

(b) admixing a liquid unsaturated compound with the molten elementalsulphur in an amount in the range of from 0.01 to 10.0 wt % based on theweight of sulphur to allow the organic polysulphide and/or thiol toreact with the unsaturated compound.

DETAILED DESCRIPTION OF THE INVENTION

In the process according to the invention, a liquid unsaturated compoundis admixed with a molten stream of elemental sulphur that contains anorganic polysulphide and/or a thiol at a temperature in the range offrom 120 to 160° C. Thus, the organic polysulphide and/or thiol isallowed to react with the unsaturated compound in order to remove thesulphide smell caused by the presence of the organic polysulphide and/orthiol.

Reference herein to an organic polysulphide is to a compound comprisinga chain of sulphur atoms with an organic radical covalently-bound withan carbon atom to each end of the chain. Such compounds have the generalmolecular formula X—S_(n)—X′, wherein n is an integer with a value of atleast 2, and X and X′ are, independently, an organic radical that isbound with a carbon atom to the sulphur chain S_(n). Typically, X and X′each are an alkyl radical.

Reference herein to a thiol is to a compound of the general molecularformula R—SH, wherein R is an organic radial, typically an alkyl radicalsuch as methyl, ethyl, propyl, isopropyl or butyl, that is bound with acarbon atom to the sulphur atom.

Reference herein to an unsaturated compound is to a compound having anaromatic or an olefinic group. The compound may have both an aromaticand an olefinic group, such as for example styrene. Cycloalkanes withouta double bond, such as for examples cyclohexane, are not considered anunsaturated compounds in this respect.

Reference herein to a liquid unsaturated compound is to an unsaturatedcompound that is liquid at the conditions at which the compound isadmixed with the molten elemental sulphur in step (b).

In step (a) of the process according to the invention, a molten streamof elemental sulphur comprising an organic polysulphide and/or a thiolis provided at a temperature in the range of from 120 to 160° C. In step(b) of the process according to the invention, a liquid unsaturatedcompound is admixed with the molten elemental sulphur in an amount inthe range of from 0.01 to 10.0 wt % based on the weight of sulphur toallow the organic polysulphide and/or thiol to react with theunsaturated compound.

The stream of elemental sulphur is provided at a temperature in therange of from 120 to 160° C. in order to have a good miscibility withthe liquid unsaturated compound. At temperatures below 120° C.,elemental sulphur is in its solid state. At temperatures above 160° C.the sulphur viscosity increases due to polymerisation reactions,therewith importantly reducing the miscibility.

The admixing in step (b) may be carried out at any suitable pressure.The pressure applied will mainly depend on the boiling point of thecompound that is admixed with the elemental sulphur. If that compoundhas a boiling point below the temperature of the molten elementalsulphur, an elevated pressure will be applied in step (b) in order tomaintain the compound in the liquid phase.

The unsaturated compound may be any compound that reacts withpolysulphides and thiols at a temperature in the range of from 120 to160° C. Preferably, the unsaturated compound is a hydrocarbon, i.e. acompound consisting of carbon and hydrogen atoms without heteroatomslike sulphur, oxygen or nitrogen. Preferably, the unsaturated compoundhas at most 20 carbon atoms, more preferably in the range of from 4 to14 carbon atoms.

Olefinic compounds that are known to be suitable as modifier orplasticizer for elemental sulphur appear to be particularly suitablecompounds for the process according to the invention. Examples of suchcompounds are styrene, dicyclopentadiene, 5-ethylidene-2-norbordene,5-vinyl-2-norbordene, 1-dodecene, 1-decene, dipentene, limonene. Anadvantage of using such compounds is that the resulting treatedelemental sulphur may be used as binder in sulphur cement or a sulphurcement-aggregate composites. As a result less or no additional sulphurmodifiers (also referred to a sulphur plasticizers) need to be added tothe sulphur binder.

Also aromatic compounds without an olefinic functionality are suitablecompounds for the process according to the invention. Examples ofparticularly suitable aromatic compounds are benzene, ethyl benzene,toluene and naphthalene.

The unsaturated compound may be admixed with the molten elementalsulphur in an amount in the range of from 0.01 to 10.0 wt %, preferablyof from 0.05 to 5.0 wt %, more preferably in the range of from 0.1 to4.0 wt % based on the weight of sulphur.

The time period during which the organic polsulphide(s) and/or thethiol(s) present in the molten elemental sulphur are allowed to reactwith the unsaturated compound in step (b) is preferably at least 5minutes, more preferably 30 minutes. It will be appreciated that theadmixing time in step (b) needs to be sufficient for the organicpolsulphide(s) and/or the thiol(s) to be removed in order to achievesufficient smell improvement. The optimum admixing time will depend onthe concentration of the organic polysulphide and thiol in the elementalsulphur and the reactivity of the unsaturated compound used.

The elemental sulphur comprising an organic polysulphide and/or a thiolmay be obtained from any source. A particularly suitable example ofelemental sulphur that comprises organic polysulphides is the stream ofelemental sulphur that may be withdrawn from a process of selectiveoxidation of hydrogen sulphide as is described in WO2005/030638. If thefeed gas for the selective oxidation process comprises one or morethiols and the selective oxidation process is carried out in a liquidelemental sulphur phase, then the elemental sulphur that is dischargedfrom the process comprises organic polysulphides, typicallyalkylpolysulphides, formed from the reaction of alkanethiols withelemental sulphur.

Therefore, the process according to the invention preferably furthercomprises the following steps:

(c) supplying a gaseous feed stream comprising hydrogen sulphide and athiol and a molecular-oxygen containing gas to a reaction zonecomprising liquid elemental sulphur and particulate oxidation catalystat a temperature in the range of from 120 to 160° C. to selectivelyoxidise hydrogen sulphide to elemental sulphur; and

(d) discharging a stream of elemental sulphur comprising polysulphidesfrom the reaction zone,

wherein the stream of elemental sulphur discharged from the reactionzone in step (c) is treated according to steps (a) and (b).

Process conditions and oxidation catalysts suitable for selectiveoxidation step (c) are described in more detail in WO2005/030638.

An alternative way to obtain a stream of elemental sulphur comprising anorganic polysulphide and/or a thiol is by contacting a thiol-loadedpurge gas from a thiol absorber with liquid elemental sulphur at atemperature in the range of from 120 to 160° C. Under these conditions,at least part of the thiols is converted into organic polysulphides. Theconversion is preferably carried out in the presence of molecular oxygenand a particulate oxidation catalyst. The stream of elemental sulphurthus obtained comprises organic polysulphide and typically alsounconverted thiol and may suitably be used in the process according tothe invention.

The treated elemental sulphur obtained with steps (a) and (b) may beused for any known application of elemental sulphur. A particularlysuitable application for the treated elemental sulphur is its use asbinder in sulphur cement or a sulphur cement-aggregate composite. It isan advantage that the presence of carbon-containing compounds, such asthe reaction product of the organic polysulphides or thiols with theunsaturated compound, is allowed in this application.

Sulphur used as binder may be modified or plasticised in order toprevent allotropic transformation of the solid sulphur. Modified sulphuris typically prepared by reacting a portion of the sulphur with asulphur modifier, also referred to as sulphur plasticiser. Modifiers aretypically added in an amount in the range of from 0.05 to 25 wt % basedon the weight of sulphur, usually in the range of from 0.1 to 10 wt %. Awell-known category of sulphur modifiers, are olefinic compounds thatco-polymerise with sulphur. Known examples of such olefinic sulphurmodifiers are dicyclopentadiene, limonene, styrene.

Sulphur cement is known in the art and at least comprises sulphur,usually in an amount of at least 50 wt %, and a filler. Usual sulphurcement fillers are particulate inorganic materials with an averageparticle size in the range of from 0.1 μm to 0.1 mm. Examples of suchsulphur cement fillers are fly ash, limestone, quartz, iron oxide,alumina, titania, graphite, gypsum, talc, mica or combinations thereof.The filler content of sulphur cement may vary widely, but is typicallyin the range of from 5 to 50 wt %, based on the total weight of thecement.

A sulphur cement-aggregate composite is a composite comprising bothsulphur cement and aggregate. Examples of sulphur cement-aggregatecomposites are sulphur mortar, sulphur concrete and sulphur-extendedasphalt. Mortar comprises fine aggregate, typically with particleshaving an average diameter between 0.1 and 5 mm, for example sand.Concrete comprises coarse aggregate, typically with particles having anaverage diameter between 5 and 40 mm, for example gravel or rock.Sulphur-extended asphalt is asphalt, i.e. aggregate with a bindercontaining filler and a residual hydrocarbon fraction, wherein part ofthe binder has been replaced by sulphur.

Accordingly, the process according to the invention preferably furthercomprises the following steps:

(e) admixing the elemental sulphur treated according to steps (a) and(b) with at least any one of a sulphur cement filler, a sulphurmodifier, or aggregate at a temperature at which sulphur is molten; and

(f) solidifying the mixture obtained by cooling the mixture to atemperature below the melting temperature of sulphur to obtain modifiedsulphur, sulphur cement or a sulphur cement-aggregate composite.

If only a sulphur modifier is admixed with the treated sulphur in step(e), modified sulphur is obtained. If a sulphur cement filler and,optionally, a sulphur modifier is admixed, sulphur cement is obtained.If both a sulphur cement filler and aggregate are admixed, optionallytogether with a sulphur modifier, sulphur mortar or sulphur concrete areobtained. Preferably, the heat-treated elemental sulphur is admixed instep (e) with at least a sulphur cement filler and sulphur cement or asulphur cement-aggregate composite is obtained in step (f).

In a preferred embodiment of the process according to the invention, thestream of elemental sulphur that is treated in steps (a) and (b) is astream of elemental sulphur that is discharged from a reaction zone forselective oxidation step (c) and the treated elemental sulphur obtainedafter steps (a) and (b) is converted into modified sulphur, sulphurcement or a sulphur cement-aggregate composite according to steps (e)and (f). In a particularly preferred embodiment, the stream of elementalsulphur that is discharged from the reaction zone for selectiveoxidation step (c) comprises at least part of the particulate oxidationcatalyst. The catalyst-comprising elemental sulphur is then treated insteps (a) and (b). Thus, a treated catalyst-comprising elemental sulphuris obtained that is converted into sulphur cement or a sulphurcement-aggregate composite according to steps (e) and (f). An advantageof this embodiment is that there is no need to separate elementalsulphur from the catalyst particles after selective oxidation step (c).As a consequence, very small catalyst particles may be used in selectiveoxidation step (c).

EXAMPLES

The invention is further illustrated by means of the followingnon-limiting examples. Throughout the examples, flow rates of gaseousstreams are expressed in Nl/hr, which stands for normal litres per hour.Normal litres are litres at conditions of standard temperature andpressure, i.e. 0° C. and 1 bar (absolute).

Example 1 (Styrene Addition; According to the Invention)

Elemental sulphur comprising organic polysulphides was obtained asfollows:

A 500 mL autoclave was loaded with 300 grams of elemental sulphur and 20grams of small particles (average particle diameter is 10 μm) of ironoxide catalyst.

The iron oxide catalyst was prepared as follows. Silica extrudateshaving a surface area of 358 m²/g as measured by nitrogen adsorption(according to the BET method) and a pore volume of 1.34 ml/g as measuredby mercury intrusion were provided with hydrated iron oxide. 100 gramsof the silica extrudates were impregnated with 134 ml of a solutionprepared from 28.6 grams of ammonium iron citrate (containing 17.5 wt %iron) and de-ionized water. The impregnated material was rotated for 90minutes to allow equilibration. The material was subsequently dried at60° C. for 2 hours, followed by drying at 120° C. for 2 hours andcalcinations in air at 500° C. for 1 hour. The initial colour of thecatalyst was black, but turned into rusty brown due to hydration of ironoxide. The resulting catalyst had a surface area of 328 m²/g, a porevolume of 1.1 ml/g and an iron content of 4.7 wt % based on the totalcatalyst weight.

The autoclave was then pressurised with nitrogen to a pressure of 40 bar(absolute) and the temperature was raised to 140° C. A stream ofnitrogen containing 650 ppmV of methanethiol was bubbled through theautoclave at a flow rate of 33 Nl/kg sulphur/hr during 150 hours. Then,a stream of pentane comprising 1.0 wt % butanethiol was supplied at afeed rate of 1.5 ml/hr whilst nitrogen bubbled through the autoclave ata flow rate of 39 Nl/kg sulphur/hr during 100 hours. The autoclave wasthen depressurised and the catalyst particles separated from theelemental sulphur by filtration.

Gas chromatography analysis of the gaseous effluent and PyrolysisCombustion Mass spectrometric Elemental analysis (PCME analysis) of theelemental sulphur showed that 98 wt % of the butanethiol and 70 wt % ofthe methanethiol were converted into organic polysulphides. The organicalkylpolysulphide content of the elemental sulphur was calculated to be0.1 wt %. The elemental sulphur had a very strong sulphide smell.

Styrene Treatment

Thirty grams of the polysulphide-comprising elemental sulphur preparedas described above was loaded in an autoclave. The autoclave waspressurised to 5 bar (absolute) and heated to 135° C. A quantity of 100μL styrene was added to the sulphur under continuous stirring. Theautoclave was kept at this temperature and pressure for 1.5 hours undercontinuous stirring. The autoclave was then cooled and de-pressurisedand the smell of a sample of the elemental sulphur was assessed. Then,the autoclave was closed again, pressurised to 5 bar (absolute) andheated to 135° C. and a further 100 μL of styrene was added and theconditions maintained for another 1.5 hours. The autoclave was thencooled and de-pressurised and the smell of a sample of the elementalsulphur was assessed. This was repeated until a total amount of 1000 μLof styrene was added.

Example 2 (Addition of 1-decene/1-dodecene Mixture; According to theInvention)

Ten grams of polysulphide-comprising elemental sulphur prepared asdescribed in EXAMPLE 1 was loaded in an autoclave. The autoclave waspressurised to 5 bar (absolute) and heated to 135° C. A quantity of 300μL of a 50/50 mixture of 1-decene and 1-dodecene was added to thesulphur under continuous stirring. The autoclave was kept at thistemperature and pressure for 1.5 hours under continuous stirring. Theautoclave was then cooled and de-pressurised and the smell of a sampleof the elemental sulphur was assessed.

Example 3 (Ethyl Benzene Addition; According to the Invention)

Elemental sulphur comprising organic polysulphides was obtained asfollows:

In a slurry bubble column were loaded 25 grams of elemental sulphur and2.20 grams of small particles (average particle diameter is 10 μm) ofiron oxide catalyst. The catalyst particles were prepared as describedin EXAMPLE 1. The column was heated to 130° C. and pressurised to 20 bar(absolute). Nitrogen was bubbled through the column at a flow rate of15.6 Nl/hr and 1 wt % butanethiol in pentane was added at a flow rate of0.025 ml/min for 100 hours. After 100 hours, a small quantity of oxygen(4 vol % oxygen in helium) was supplied to the column in order to removethe hydrogen sulphide that was formed in the conversion of butanethiol(by selectively oxidising the hydrogen sulphide into elemental sulphur).Then, the column was cooled to room temperature, depressurised to 1 bar(absolute) and the catalyst and the treated sulphur were unloaded. Thecatalyst particles were separated from the elemental sulphur byfiltration. The butanethiol content of the elemental sulphur wasdetermined by Pyrolysis Combustion Mass spectrometric Elemental analysis(PCME analysis). This analysis showed that 99 wt % of the butanethiolsupplied to the reactor was converted into organic polysulphides. Thealkylpolysulphide content of the elemental sulphur was calculated to be0.4 wt %. The elemental sulphur had a pronounced sulphide smell.

Ethyl Benzene Treatment

Fifteen grams of polysulphide-comprising elemental sulphur prepared asdescribed above was loaded in an autoclave. The autoclave waspressurised to 5 bar (absolute) and heated to 135° C. A quantity of 120μL ethyl benzene was added to the sulphur under continuous stirring. Theautoclave was kept at this temperature and pressure for 1.5 hours undercontinuous stirring. The autoclave was then cooled and de-pressurisedand the smell of a sample of the elemental sulphur was assessed.

Example 4 (Benzene Addition; According to the Invention)

Fifteen grams of polysulphide-comprising elemental sulphur prepared asdescribed above was loaded in an autoclave. The autoclave waspressurised to 5 bar (absolute) and heated to 135° C. A quantity of 145μL benzene was added to the sulphur under continuous stirring. Theautoclave was kept at this temperature and pressure for 1.5 hours undercontinuous stirring. The autoclave was then cooled and de-pressurisedand the smell of a sample of the elemental sulphur was assessed.

Example 5 (Dodecane Addition; Not According to the Invention)

Fifteen grams of polysulphide-comprising elemental sulphur prepared asdescribed above was loaded in an autoclave. The autoclave waspressurised to 5 bar (absolute) and heated to 135° C. A quantity of 160μL dodecane was added to the sulphur under continuous stirring. Theautoclave was kept at this temperature and pressure for 1.5 hours undercontinuous stirring. The autoclave was then cooled and de-pressurisedand the smell of a sample of the elemental sulphur was assessed.

The smell of the treated elemental sulphur of EXAMPLES 1 to 5 is givenin the Table.

TABLE Effect of addition of an unsaturated compound on sulphide smellSulphide Concentration smell of added treated Compound compound onelemental added Amount sulphur (wt %) sulphur none 0 0 very strongstyrene 0.1 ml^(a) 0.3 weak styrene 0.23 ml^(a) 0.7 very weak styrene0.7 ml^(a) 2.1 very weak styrene 1.0 ml^(a) 3.0 negligible 1-decene/ 0.3ml^(b) 2.3 negligible 1-dodecene mixture ethyl 0.12 ml^(c) 0.7 weakbenzene benzene 0.145 ml^(c) 0.8 weak dodecane 0.16 ml^(c) 0.9 verystrong (comparison) ^(a)to 30 grams of polysulphide containing elementalsulphur ^(b)to 10 grams of polysulphide containing elemental sulphur^(c)to 15 grams of polysulphide containing elemental sulphur

1. A process for treating a stream of elemental sulphur comprising anorganic polysulphide for smell improvement, the process comprising thefollowing steps: (a) providing a molten stream of elemental sulphurcomprising an organic polysulphide at a temperature in the range of from120 to 160° C.; (b) admixing a liquid unsaturated compound with thestream of molten elemental sulphur in an amount in the range of from0.01 to 10.0 wt % based on the weight of sulphur to allow the organicpolysulphide to react with the unsaturated compound; and furthercomprising the following steps (c) supplying a gaseous feed streamcomprising hydrogen sulphide and a thiol and a molecular-oxygencontaining gas to a reaction zone comprising liquid elemental sulphurand particulate oxidation catalyst at a temperature in the range of from120 to 160° C. to selectively oxidise hydrogen sulphide to elementalsulphur; and (d) discharging a stream of elemental sulphur comprising anorganic polysulphide from the reaction zone; wherein the stream ofelemental sulphur discharged from the reaction zone in step (d) istreated according to steps (a) and (b).
 2. A process according to claim1, wherein the unsaturated compound is a hydrocarbon.
 3. A processaccording to claim 1, wherein the unsaturated compound has at most 20carbon atoms.
 4. A process according to claim 2, wherein the unsaturatedcompound is a hydrocarbon selected from styrene, dicyclopentadiene,5-ethylidene-2-norbordene, 5-vinyl-2-norbordene, ethyl benzene,1-dodecene, 1-decene, dipentene, limonene, benzene, or toluene.
 5. Aprocess according to claim 1, wherein the unsaturated compound is asulphur modifier.
 6. A process according to claim 1, wherein theunsaturated compound is admixed with the molten elemental sulphur in anamount in the range from 0.05 to 5.0 wt % based on the weight ofsulphur.
 7. A process according to claim 1, wherein the organicpolysulphide is allowed to react with the unsaturated compound for atleast 5 minutes.
 8. A process according to claim 1, further comprisingthe following steps: (e) admixing the elemental sulphur treatedaccording to steps (a) and (b) with at least any one of a sulphur cementfiller, a sulphur cement modifier, or aggregate at a temperature atwhich sulphur is molten; and (f) solidifying the mixture obtained bycooling the mixture to a temperature below the melting temperature ofsulphur to obtain modified sulphur, sulphur cement or a sulphurcement-aggregate composite.
 9. A process according to claim 8, whereinthe treated elemental sulphur is admixed in step (e) with at least asulphur cement filler and sulphur cement or a sulphur cement-aggregatecomposite is obtained in step (f).
 10. A process according to claim 7 ,wherein the stream of elemental sulphur discharged from the reactionzone in step (d) and treated according to steps (a) and (b) comprisesparticulate oxidation catalyst.
 11. A process for treating a stream ofelemental sulphur comprising an organic polysulphide and a thiol, forsmell improvement, the process comprising the following steps: (a)providing a molten stream of elemental sulphur comprising an organicpolysulphide and a thiol, at a temperature in the range of from 120 to160° C.; (g) admixing a liquid unsaturated compound with the stream ofmolten elemental sulphur in an amount in the range of from 0.01 to 10.0wt % based on the weight of sulphur to allow the organic polysulphideand the thiol, to react with the unsaturated compound; and furthercomprising the following steps (h) supplying a gaseous feed streamcomprising hydrogen sulphide and a thiol and a molecular-oxygencontaining gas to a reaction zone comprising liquid elemental sulphurand particulate oxidation catalyst at a temperature in the range of from120 to 160° C. to selectively oxidise hydrogen sulphide to elementalsulphur; and (i) discharging a stream of elemental sulphur comprising anorganic polysulphide from the reaction zone; wherein the stream ofelemental sulphur discharged from the reaction zone in step (d) istreated according to steps (a) and (b).
 12. A process according to claim2, wherein the unsaturated compound has at most 20 carbon atoms.
 13. Aprocess according to claim 1, wherein the unsaturated compound has inthe range of from 4 to 14 carbon atoms.
 14. A process according to claim2, wherein the unsaturated compound has in the range of from 4 to 14carbon atoms.
 15. A process according to claim 3, wherein theunsaturated compound is a hydrocarbon selected from styrene,dicyclopentadiene, 5-ethylidene-2-norbordene, 5-vinyl-2-norbordene,ethyl benzene, 1-dodecene, 1-decene, dipentene, limonene, benzene, ortoluene.
 16. A process according to claim 12, wherein the unsaturatedcompound is a hydrocarbon selected from styrene, dicyclopentadiene,5-ethylidene-2-norbordene, 5-vinyl-2-norbordene, ethyl benzene,1-dodecene, 1-decene, dipentene, limonene, benzene, or toluene.
 17. Aprocess according to claim 13, wherein the unsaturated compound is ahydrocarbon selected from styrene, dicyclopentadiene,5-ethylidene-2-norbordene, 5-vinyl-2-norbordene, ethyl benzene,1-dodecene, 1-decene, dipentene, limonene, benzene, or toluene.
 18. Aprocess according to claim 14, wherein the unsaturated compound is ahydrocarbon selected from styrene, dicyclopentadiene,5-ethylidene-2-norbordene, 5-vinyl-2-norbordene, ethyl benzene,1-dodecene, 1-decene, dipentene, limonene, benzene, or toluene.
 19. Aprocess according to claim 1, wherein the unsaturated compound isstyrene, dicyclopentadiene, 5-ethylidene-2-norbordene,5-vinyl-2-norbordene, 1-dodecene, 1-decene, dipentene, or limonene. 20.A process according to claim 1, wherein the unsaturated compound isadmixed with the molten elemental sulphur in an amount in the range offrom 0.1 to 4.0 wt % based on the weight of sulphur.